Washing machine and control method thereof

ABSTRACT

A washing machine having a boiling washing course function to perform washing by heating water to increase a washing effect, and a control method thereof. In the washing machine and control method, it is possible to increase a washing effect by heating water for a predetermined time according to the temperature of the initially supplied water, draining the water if the temperature of the heated water is less than the set temperature, and maintaining the amount of the initially supplied water without draining the water if the temperature of the water is equal to or greater than the set temperature. Further, by allowing the water to reach the target temperature of a high temperature within a predetermined washing time while maintaining the amount of the initially supplied water, it is possible to maintain a washing effect due to a washing temperature thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2013-0108819, filed on Sep. 11, 2013 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND

1. Field

Embodiments of the present disclosure relate to a washing machine havinga boiling washing course function to perform washing by heating water inorder to increase a washing effect, and a control method thereof.

2. Description of the Related Art

In general, a washing machine (e.g., fully automatic washing machine)includes a tub to accommodate water (washing water or rinsing water), awashing tub rotatably installed inside the tub to accommodate thelaundry and a pulsator rotatably installed inside the washing tub togenerate a water flow, and a motor to generate driving force forrotating the washing tub and the pulsator. The washing machine is anapparatus for removing stains from laundry by surface activity of adetergent and a water flow.

This washing machine performs washing by a series of operations such asa washing process to separate stains from the laundry using water(specifically, washing water) in which a detergent is dissolved, arinsing process to rinse a residual detergent or bubbles out of thelaundry using water (specifically, rinsing water) which does not containa detergent, and a spin-dry process to remove water contained in thelaundry by high speed rotation.

Among the above-mentioned processes, the washing process has a boilingwashing course function to perform washing by heating supplied water inorder to increase a washing effect of contaminated laundry.

In a conventional boiling washing course, initially supplied water isheated and the water is unconditionally drained when the temperature(water temperature) of the water reaches a set temperature. Then, afterthe water level is reduced to be lower than the level of the initiallysupplied water, the water is heated up to a target temperature. This isintended to reduce electrical energy consumed for heating the waterbecause plenty of water is used due to the nature of the fully automaticwashing machine.

However, in the conventional boiling washing course, since the water isunconditionally drained although the level of the initially suppliedwater is the amount of washing water suitable for the laundry, theamount of the detergent and the initially supplied water for washing thecontaminated laundry decreases, and the washing effect may be reduced.

SUMMARY

Therefore, it is an aspect of the present disclosure to provide awashing machine capable of increasing a washing effect by heatinginitially supplied water for a predetermined time, determining whetherto drain water according to the temperature of the water, andmaintaining the amount of the initially supplied water withoutunconditionally draining the water, and a control method thereof.

Additional aspects of the disclosure will be set forth in part in thedescription which follows and, in part, will be apparent from thedescription, or may be learned by practice of the disclosure.

In accordance with one aspect of the present disclosure, a controlmethod of a washing machine including a tub to accommodate water and aheater installed inside the tub to heat the water includes determiningwhether a currently washing course is a boiling washing course,supplying water into the tub if the currently washing course is theboiling washing course, performing primary heating washing to heat thesupplied water for a predetermined time, detecting a temperature of theprimarily heated water, and controlling a level of water in the tub forsecondary heating washing according to the detected temperature of thewater. The controlling the water level includes varying the level ofwater in the tub according to the temperature of the primarily heatedwater.

The controlling the water level may include comparing the temperature ofthe primarily heated water with a set temperature, and maintaining acurrent water level without draining the primarily heated water if thetemperature of the primarily heated water is greater than the settemperature.

Further, if the temperature of the primarily heated water is equal to orless than the set temperature, the primarily heated water may be drainedto lower the water level.

The supplying the water into the tub may include supplying water up to apredetermined water level for the boiling washing course.

The supplied water may be cold water or hot water.

The performing the primary heating washing may include detecting atemperature of the water supplied into the tub, determining a primaryheating time according to the detected temperature of the water, anddriving the heater according to the determined primary heating time.

The draining the water may include draining the water down to a waterlevel lower by one level than the predetermined water level.

Further, the control method may further include performing secondaryheating washing to heat the primarily heated water up to a targettemperature after controlling the water level.

The set temperature may be a temperature of the water supplied up to thepredetermined water level, which may reach the target temperature withina secondary heating time, and the set temperature may be about 45° C.

The target temperature may be equal to or greater than 70° C. which mayprovide a boiling effect.

Further, the control method may further include performing washing for aset time after the secondary heating washing.

Further, the control method may further include performing a coolingprocess by supplying cold water after performing the washing.

Further, the control method may further include performing a washing andcooling process by supplying cold water after performing the secondaryheating washing.

In accordance with another aspect of the present disclosure, a controlmethod of a washing machine includes a tub to accommodate water and aheater installed inside the tub to heat the water determining whether acurrently washing course is a boiling washing course, supplying waterinto the tub if the currently washing course is the boiling washingcourse, detecting a temperature of the supplied water, determining aprimary heating time according to the detected temperature of the water,performing primary heating washing by driving the heater according tothe determined primary heating time, and controlling a level of water inthe tub for secondary heating washing according to the detectedtemperature of the water. The controlling the water level includesvarying the level of water in the tub according to the temperature ofthe supplied water.

The controlling the water level may include comparing the temperature ofthe supplied water with a set temperature, and maintaining a currentwater level without draining the primarily heated water if thetemperature of the supplied water is greater than the set temperature.

Further, the controlling the water level may include comparing thetemperature of the supplied water with a set temperature, and loweringthe water level by draining the primarily heated water if thetemperature of the supplied water is equal to or less than the settemperature.

Further, the control method may further include, after controlling thewater level, performing secondary heating washing to heat the primarilyheated water up to a target temperature.

In accordance with one aspect of the present disclosure, a washingmachine includes a tub to accommodate water, a heater installed insidethe tub to heat the water, an input unit through which a boiling washingcourse is selected, a control unit to, if the boiling washing course isselected, perform primary heating washing for a predetermined time aftersupplying water into the tub, detect a temperature of the primarilyheated water, and control a level of water in the tub for secondaryheating washing. The control unit may vary the level of water in the tubaccording to the temperature of the primarily heated water.

The control unit may compare the temperature of the supplied water witha set temperature, and maintain a current water level without drainingthe primarily heated water if the temperature of the supplied water isgreater than the set temperature.

Further, the control unit may compare the temperature of the suppliedwater with a set temperature, and lower the water level by draining theprimarily heated water if the temperature of the supplied water is equalto or less than the set temperature.

Further, after controlling the water level, the control unit may performsecondary heating washing to heat the primarily heated water up to atarget temperature.

In accordance with another aspect of the present disclosure, a washingmachine includes a tub to accommodate water, a heater installed insidethe tub to heat the water, an input unit through which a boiling washingcourse is selected, a control unit to, if the boiling washing course isselected, supply water into the tub, detect a temperature of thesupplied water, perform primary heating washing to drive the heater fora primary heating time determined according to the detected temperatureof the water, and control a level of water in the tub for secondaryheating washing according to the detected temperature of the water. Thecontrol unit may vary the level of water in the tub according to thetemperature of the supplied water.

The control unit may compare the temperature of the supplied water witha set temperature, and maintain a current water level without drainingthe primarily heated water if the temperature of the supplied water isgreater than the set temperature.

The control unit may compare the temperature of the supplied water witha set temperature, and lower the water level by draining the primarilyheated water if the temperature of the supplied water is equal to orless than the set temperature.

According to the proposed washing machine and control method thereof, itis possible to increase a washing effect by heating water for apredetermined time according to the temperature of the initiallysupplied water, draining the water if the temperature of the heatedwater is less than the set temperature, and maintaining the amount ofthe initially supplied water without draining the water if thetemperature of the water is equal to or greater than the settemperature. Further, by allowing the water to reach the targettemperature of a high temperature within a predetermined washing timewhile maintaining the amount of the initially supplied water, it ispossible to maintain a washing effect due to a washing temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the disclosure will become apparent andmore readily appreciated from the following description of theembodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a cross-sectional view showing a configuration of a washingmachine according to an embodiment of the present disclosure;

FIG. 2 is a control block diagram of the washing machine according tothe embodiment of the present disclosure;

FIG. 3 is a diagram showing the water levels of the washing machineaccording to the embodiment of the present disclosure;

FIGS. 4A and 4B illustrate an operation flowchart showing a firstcontrol algorithm for boiling washing in the washing machine accordingto the embodiment of the present disclosure;

FIGS. 5A and 5B illustrate an operation flowchart showing a secondcontrol algorithm for boiling washing in the washing machine accordingto the embodiment of the present disclosure;

FIGS. 6A and 6B illustrate an operation flowchart showing a thirdcontrol algorithm for boiling washing in the washing machine accordingto the embodiment of the present disclosure; and

FIGS. 7A and 7B illustrate an operation flowchart showing a fourthcontrol algorithm for boiling washing in the washing machine accordingto the embodiment of the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the presentdisclosure, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

FIG. 1 is a cross-sectional view showing a configuration of a washingmachine according to an embodiment of the present disclosure.

Referring to FIG. 1, a washing machine 1 according to the embodiment ofthe present disclosure includes a substantially box-shaped cabinet 10forming an external appearance of the washing machine 1, a tub 11installed inside the cabinet 10 to accommodate water (washing water orrinsing water), a washing tub 12 rotatably installed inside the tub 11to accommodate the laundry and a pulsator 13 rotatably installed insidethe washing tub 12 to rotate clockwise or counterclockwise (forward orbackward) and generate a water flow. The washing machine has a verticalaxis.

The washing tub 12 is formed in a cylindrical shape to have an open topportion. On the side surface of the washing tub 12, pluralwater-extracting holes 12 a are formed. A balancer 12 b may be installedin an upper portion of the washing tub 12 such that the washing tub 12may be rotated stably during high-speed rotation.

On the lower outside of the tub 11, there are installed a washing motor14 to generate a driving force for rotating the washing tub 12 and thepulsator 13, and a power switching device 15 to simultaneously orselectively transfer the driving force generated from the washing motor14 to the washing tub 12 and the pulsator 13.

A hollow water-extracting shaft 16 is coupled to the washing tub 12. Awashing shaft 17 is installed in the hollow portion of thewater-extracting shaft 16. The washing shaft 17 may be coupled to thepulsator 13 through a washing shaft coupling part 18.

The washing motor 14 is a direct drive (DD) motor having a variablespeed function. The washing motor 14 may selectively transfer drivingforce to the washing tub 12 or the pulsator 13 according to verticalmovements.

Further, as the washing motor 14, a universal motor including a fieldcoil and an armature, a brushless direct current (BLDC) motor includinga stator and a rotor, or the like may be used. In addition, any motorwhich is applicable to the washing machine 1 may be used. Alternatively,the washing motor 14 may be configured in a belt manner.

A water outlet port 20 is formed at the bottom of the tub 11 todischarge water to the outside, and a first drain pipe 21 is connectedto the water outlet port 20. A drain motor 22 is installed in the firstdrain pipe 21 to regulate drainage. A second drain pipe 23 fordischarging water to the outside is connected to the outlet of the drainmotor 22.

Further, on the lower inside of the tub 11, there are installed a heater30 to heat the water in the tub 11, a temperature sensor 32 to detectthe temperature of the water in the tub 11, and a water level sensor 34to detect a frequency varying according to the water level in order todetect the amount of water (water level) in the tub 11.

On the upper side of the cabinet 10, there are installed a door 40 whichis opened/closed to load laundry into the washing tub 12 or unload thelaundry from the washing tub 12, and a top cover 42 which the door 40 isseparated from or seated on according to whether the door 40 is openedor closed.

At the top cover 42, there is formed a laundry input port 46 throughwhich the laundry is loaded into the washing tub 12 or the laundry isunloaded from the washing tub 12. The laundry input port 46 may beopened and closed by the door 40.

Further, a detergent box 48 for supplying a detergent and softeningagent and a water supply device 50 for supplying water (washing water orrinsing water) are installed in the upper part of the cabinet 10.

The water supply device 50 includes first and second water supply pipes51 and 52 which connect an external water supply pipe to the detergentbox 48 to supply water (washing water or rinsing water) into the tub 11,and first and second water supply valves 53 and 54 which are installedin the first and second water supply pipes 51 and 52 to control thesupply of hot or cold water. This configuration enables the watersupplied into the tub 11 to pass through the detergent box 48 so thatthe detergent may be supplied together with the water into the tub 11.

FIG. 2 is a control block diagram of the washing machine according tothe embodiment of the present disclosure.

Referring to FIG. 2, the washing machine 1 according to the embodimentof the present disclosure is configured to include an input unit 70, acontrol unit 72, a memory 74, a driving unit 76 and a display unit 78.

The input unit 70 enables the user to input a command for performing awashing process, a rinsing process, a spin-dry process and the like ofthe washing machine 1. The input unit 70 may be configured as keys,buttons, switches, touch pads and the like, and includes all devices togenerate predetermined input data by an operation (e.g., pressing,touching, pressure and rotation).

Further, the input unit 70 includes a plurality of buttons (power,reservation, washing, rinsing, water-extraction, water level selection,etc.) for entering a user command related to operation of the washingmachine 1. Among the plurality of buttons, there are provided courseselection buttons for selecting a washing course (standard course, woolcourse, boiling course, etc.) depending on the type of laundry loaded inthe washing machine 1.

The course selection buttons provided in the input unit 70 include aboiling course button 71 to select a boiling washing course forperforming washing by heating the supplied water in order to increase awashing effect on the contaminated laundry.

The boiling course button 71 is provided to perform washing by heatingthe supplied water in the case of requiring a sterilization effect aswell as removal of stains and odors from laundry such as baby clothesand underwear. The boiling course does not require the water to beheated to a boiling point, i.e. 100° C.

The control unit 72 is a microcomputer for controlling the overalloperations of the washing machine 1 such as washing, rinsing andspin-dry operations according to the operating information inputted fromthe input unit 70. The control unit 72 sets the amount of water forwashing and rinsing, a target RPM, a motor operation rate (washing motoron-off time), washing and rinsing time and the like according to theweight (load) of the laundry in the selected washing course.

Further, the control unit 72 controls a driving timing and driving timeof a heater 30 to maximize washing effects by heating the supplied waterduring boiling washing.

Accordingly, if a boiling washing course is selected, the control unit72 performs primary heating washing for a predetermined washing time bydriving the washing motor 14 and the heater 30 after supplying water upto a second water level (middle water level) determined for a boilingwashing course. The primary heating time varies depending on thetemperature (water temperature) of primarily heated water. As the watertemperature is higher, the primary heating time is shorter. When theprimary heating time has elapsed, the primary heating washing is stoppedby stopping the washing motor 14 and the heater 30.

Then, the control unit 72 determines whether to drain water according tothe temperature of the primarily heated water. That is, the control unit72 determines whether the temperature of the primarily heated water is awater temperature (third temperature; about 45° C.) that may reach atarget temperature Ts within a secondary heating time, and determineswhether to drain water.

For example, if the temperature of the primarily heated water is equalto or less than the third temperature, the control unit 72 performssecondary heating washing to heat the water up to the target temperatureby driving the washing motor 14 and the heater 30 again after drainingwater down to a first water level (low water level).

On the other hand, if the temperature of the primarily heated water isgreater than the third temperature, the control unit 72 performssecondary heating washing to heat the water up to the target temperatureTs by driving the washing motor 14 and the heater 30 again whilemaintaining the second water level of the primarily heated water withoutdraining the water.

Thus, the control unit 72 performs a boiling course process to increasethe washing effect by determining whether to drain water according tothe water temperature after heating the primarily heated water forboiling washing, and maintaining the amount of the primarily heatedwater without unconditionally draining the water.

The memory 74 may store control data for controlling the operation ofthe washing machine 1, reference data used during the control of theoperation of the washing machine 1, operation data generated while thewashing machine 1 performs a predetermined operation, settinginformation such as setting data inputted via the input unit 70 toenable the washing machine 1 to perform a predetermined operation, useinformation including the number of times the washing machine 1 performsa specific operation and model information of the washing machine 1, andfailure information including the cause or location of the malfunctionwhen the washing machine 1 malfunctions.

The driving unit 76 drives the washing motor 14, the drain motor 22, theheater 30, the first water supply valve 53, the second water supplyvalve 54 and the like relating to the operation of the washing machine 1according to a driving control signal of the control unit 72.

The display unit 78 displays the operating state of the washing machine1 and the operation status of the user according to a display controlsignal of the control unit 72.

Hereinafter, an operation process and operational effects of the washingmachine and control method thereof according to the embodiment of thepresent disclosure will be described.

When the user intends to wash baby clothes and underwear, the userdesires to perform boiling washing such that bacteria in the laundry maybe sterilized while removing stains and odors from the laundry.Accordingly, in the present disclosure, a boiling washing course capableof further increasing the washing effect compared to conventional caseswhile satisfying user demands will be described with reference to FIGS.3 to 7.

FIG. 3 is a diagram showing the water levels of the washing machineaccording to the embodiment of the present disclosure.

In FIG. 3, the levels of water supplied into the tub 11 are representedas three water levels. The first water level is the lowest water levelof 12 L, the second water level is the middle water level of 18 L, andthe third water level is the highest water level of 27 L.

FIGS. 4A and 4B illustrate an operation flowchart showing a firstcontrol algorithm for boiling washing in the washing machine accordingto the embodiment of the present disclosure.

Referring to FIGS. 4A and 4B, if the user loads the laundry(specifically, baby clothes) into the washing tub 12 and selects theboiling course button 71 provided in the input unit 70 (operation 100),the operation information selected by the user is inputted to thecontrol unit 72 through the input unit 70.

Accordingly, the control unit 72 operates the first water supply valve53 or the second water supply valve 54 through the driving unit 76 inorder to supply water (washing water) required for the boiling washingprocess. In this case, the operation of the first water supply valve 53or the second water supply valve 54 varies according to the water supplyof hot water or cold water selected by the user.

For example, the first water supply valve 53 is operated if the userselects hot water, and the second water supply valve 54 is operated ifthe user selects cold water. If the user selects hot and cold water, thefirst water supply valve 53 and the second water supply valve 54 areoperated.

If the first water supply valve 53 or the second water supply valve 54is operated, the first water supply valve 53 or the second water supplyvalve 54 is opened, and the water (washing water) supplied through theexternal water supply pipe passes through the first water supply pipe 51or the second water supply pipe 52 and the detergent box 48 and issupplied into the tub 11 together with the detergent (operation 102).

Accordingly, the control unit 72 detects the level of the water suppliedinto the tub 11 through the water level sensor 34 and determines whetherthe water level is the second water level (middle water level when thewater levels in the washing machine are divided into three water levels;about 18 L) shown in FIG. 3 (operation 104). The control unit 72continues a water supply operation until the level of the water suppliedinto the tub 11 reaches the second water level.

If the level of the water supplied into the tub 11 reaches the secondwater level through the water supply operation, the control unit 72stops the water supply operation by stopping the first water supplyvalve 53 or the second water supply valve 54.

Upon completion of the water supply up to the second water level, thecontrol unit 72 detects the temperature (water temperature T) of thewater in the tub 11 through the temperature sensor 32 (operation 106).

The control unit 72 determines whether the water temperature T detectedthrough the temperature sensor 32 is greater than 0° C. (T0) and equalto or less than a first temperature T1 (about 10° C.) (operation 108).

As the determination result of operation 108, if it is determined thatthe water temperature T is greater than 0° C. (T0) and equal to or lessthan the first temperature T1 (about 10° C.), the control unit 72determines that the water temperature T is a water temperature inwinter, and performs the primary heating washing by driving the washingmotor 14 and the heater 30 (operation 110).

In this case, the control unit 72 determines, as a first time period(about 25 minutes), a time period during which the water must be heatedto determine whether to drain water after the primary heating washingunder the winter water temperature conditions. Then, the control unit 72counts the time passed since the start of the primary heating washing,and determines whether the predetermined first time period (about 25minutes) has elapsed (operation 112).

As the determination result of operation 112, if the first time periodhas not elapsed, the control unit 72 returns to operation 110, andperforms the primary heating washing until the first time period haselapsed.

On the other hand, as the determination result of operation 112, if thefirst time period has elapsed, the control unit 72 stops the primaryheating washing by stopping the washing motor 14 and the heater 30(operation 114).

On the other hand, as the determination result of operation 108, if itis not determined that the water temperature T is greater than 0° C.(T0) and equal to or less than the first temperature T1 (about 10° C.),the control unit 72 determines whether the water temperature T detectedthrough the temperature sensor 32 is greater than the first temperatureT1 (about 10° C.) and equal to or less than a second temperature T2(about 20° C.) (operation 140).

As the determination result of operation 140, if it is determined thatthe water temperature T is greater than the first temperature T1 (about10° C.) and equal to or less than the second temperature T2 (about 20°C.), the control unit 72 determines that the water temperature T is awater temperature in spring/fall, and performs the primary heatingwashing by driving the washing motor 14 and the heater 30 (operation142).

In this case, the control unit 72 determines, as a second time period(about 20 minutes), a time period during which the water must be heatedto determine whether to drain water after the primary heating washingunder the spring/fall water temperature conditions. Then, the controlunit 72 counts the time passed since the start of the primary heatingwashing, and determines whether the predetermined second time period(about 20 minutes) has elapsed (operation 144).

As the determination result of operation 144, if the second time periodhas not elapsed, the control unit 72 returns to operation 142, andperforms the primary heating washing until the second time period haselapsed.

On the other hand, as the determination result of operation 144, if thesecond time period has elapsed, the control unit 72 proceeds tooperation 114 and stops the primary heating washing by stopping thewashing motor 14 and the heater 30.

On the other hand, as the determination result of operation 140, if itis not determined that the water temperature T is greater than the firsttemperature T1 (about 10° C.) and equal to or less than the secondtemperature T2 (about 20° C.), the control unit 72 determines whetherthe water temperature T detected through the temperature sensor 32 isgreater than the second temperature T2 (about 20° C.) (operation 150).

As the determination result of operation 150, if it is determined thatthe water temperature T is greater than the second temperature T2 (about20° C.), the control unit 72 determines that the water temperature T isa water temperature in summer, and performs the primary heating washingby driving the washing motor 14 and the heater 30 (operation 152).

In this case, the control unit 72 determines, as a third time period(about 15 minutes), a time period during which the water must be heatedto determine whether to drain water after the primary heating washingunder the summer water temperature conditions. Then, the control unit 72counts the time passed since the start of the primary heating washing,and determines whether the predetermined third time period (about 15minutes) has elapsed (operation 154).

As the determination result of operation 154, if the third time periodhas not elapsed, the control unit 72 returns to operation 152, andperforms the primary heating washing until the third time period haselapsed.

On the other hand, as the determination result of operation 154, if thethird time period has elapsed, the control unit 72 proceeds to operation114 and stops the primary heating washing by stopping the washing motor14 and the heater 30.

Thus, the primary heating washing is performed to heat the water for thefirst time period, the second time period, or the third time periodaccording to the temperature of the primarily heated water. Then, afterthe primary heating washing, whether to drain water is determinedaccording to the water temperature.

Accordingly, the control unit 72 detects the water temperature T of theprimarily heated water through the temperature sensor 32 in order todetermine whether to drain water according to the temperature of theprimarily heated water, and determines whether the detected watertemperature T is equal to or less than a predetermined third temperatureT3 (water temperature which may reach the target temperature within thesecondary heating time; about 45° C.) (operation 116).

As the determination result of operation 116, if the water temperature Tis equal to or less than the third temperature T3 (about 45° C.), thecontrol unit 72 determines that the temperature of the primarily heatedwater is not a water temperature which may reach the target temperatureTs within the second heating time (about 35 minutes), and operates thedrain motor 22 to drain the primarily heated water (washing water)(operation 118).

Accordingly, the control unit 72 detects the level of the waterremaining in the tub 11 according to the drain operation through thewater level sensor 34, determines whether the water level is the firstwater level (the lowest water level when the water levels in the washingmachine are divided into three water levels; about 12 L) shown in FIG. 3(operation 120), and continues the drain operation until the water levelreaches the first water level.

When the level of the water remaining in the tub 11 through the drainoperation reaches the first water level, the control unit 72 stops thedrain operation of the drain motor 22.

Subsequently, the control unit 72 drives the washing motor 14 and theheater 30 again and performs secondary heating washing to heat the waterup to the target temperature Ts (final target temperature capable ofproviding a boiling effect; about 90° C.) (operation 122).

On the other hand, as the determination result of operation 116, if thewater temperature T is greater than the third temperature T3 (about 45°C.), the control unit 72 determines that the temperature of theprimarily heated water is a water temperature which may reach the targettemperature Ts within the second heating time (about 35 minutes), anddoes not drain the primarily heated water.

Accordingly, the control unit 72 proceeds to operation 122 whilemaintaining the second water level of the primarily heated water, andperforms the secondary heating washing to heat the water up to thetarget temperature Ts by driving the washing motor 14 and the heater 30again.

Thus, if the water temperature increases according to the secondaryheating washing, the control unit 72 detects the water temperature T ofthe secondarily heated water through the temperature sensor 32, anddetermines whether the detected water temperature T is equal to orgreater than the predetermined target temperature Ts (operation 124).

As the determination result of operation 124, if the water temperature Tis less than the target temperature Ts, the control unit 72 returns tooperation 122, and continues the secondary heating washing until thewater temperature T reaches the target temperature Ts.

On the other hand, as the determination result of operation 124, if thewater temperature T is equal to or greater than the target temperatureTs, the control unit 72 stops the secondary heating washing by stoppingthe washing motor 14 and the heater 30 (operation 125).

Then, the control unit 72 performs washing by using high-temperaturewater (washing water) after the water temperature T reaches the targettemperature Ts (operation 126). In this case, washing is performed for aset time using high-temperature water without additional consumption ofelectricity by driving only the washing motor 14 without driving theheater 30, thereby providing a more or less boiling washing effect.

The control unit 72 counts the washing progress time in the state of thefirst water level (or second water level) in which cold water is notsupplied after the water temperature T reaches the target temperatureTs, and determines whether a fifth time period (time period during whichwashing is additionally performed after the water temperature T reachesthe target temperature Ts to increase the washing effect, about 10 to 15minutes) has elapsed (operation 128).

As the determination result of operation 128, if the fifth time periodhas not elapsed, the control unit 72 returns to operation 126, andperforms the subsequent operations.

On the other hand, as the determination result of operation 128, if thefifth time period has elapsed, the control unit 72 operates the secondwater supply valve 54 to supply cold water (operation 130). Whenhigh-temperature water is drained after the boiling washing iscompleted, there is a possibility that the user may get burned. Takingthis possibility into consideration, a cooling process is performed bysupplying cold water in the final stage of the boiling washing.

Thus, the control unit 72 detects the water level, at which cold wateris supplied into the tub 11, through the water level sensor 34, anddetermines whether the water level is the third water level (the highestwater level when the water levels in the washing machine are dividedinto three water levels; about 27 L) shown in FIG. 3 (operation 132).Then, the control unit 72 continues a water supply operation until thelevel of the water supplied into the tub 11 reaches the third waterlevel. That is, in order to reduce the temperature of the water to atemperature (about 55 to 60° C.) suitable for drainage at which there isno risk of burns when water is drained after the boiling washing, coldwater is supplied up to the third water level.

If the level of the water supplied into the tub 11 reaches the thirdwater level through the water supply operation, the control unit 72stops the cold water supply operation by closing the second water supplyvalve 54.

Upon completion of the supply of cold water up to the third water level,the control unit 72 performs a separate cooling process by driving thewashing motor 14 for a set time (about 2 minutes) (operation 134), andcompletes the washing process.

Meanwhile, in the embodiment of the present disclosure, a case ofperforming washing for a set time (about 10 to 15 minutes) usinghigh-temperature water by driving only the washing motor 14 withoutdriving the heater 30 after the water temperature T reaches the targettemperature Ts has been described as an example, but the presentdisclosure is not limited thereto. That is, washing may be performed fora set time while maintaining the target temperature Ts by driving theheater 30 as well as the washing motor 14.

Next, a method of providing a cooling effect while performing thewashing for the remaining time by supplying cold water after the watertemperature T reaches the target temperature Ts will be described withreference to FIGS. 5A and 5B.

FIGS. 5A and 5B illustrate an operation flowchart showing a secondcontrol algorithm for boiling washing in the washing machine accordingto the embodiment of the present disclosure. A repeated description ofthe same configurations as those of FIGS. 4A and 4B will be omitted.

Referring to FIGS. 5A and 5B, if the user loads the laundry(specifically, baby clothes) into the washing tub 12 and selects theboiling course button 71 provided in the input unit 70 (operation 200),the operation information selected by the user is inputted to thecontrol unit 72 through the input unit 70.

Accordingly, the control unit 72 operates the first water supply valve53 or the second water supply valve 54 through the driving unit 76 inorder to supply water (washing water) required for the boiling washingprocess.

If the first water supply valve 53 or the second water supply valve 54is operated, the first water supply valve 53 or the second water supplyvalve 54 is opened, and the water (washing water) supplied through theexternal water supply pipe passes through the first water supply pipe 51or the second water supply pipe 52 and the detergent box 48 and issupplied into the tub 11 together with the detergent (operation 202).

Accordingly, the control unit 72 detects the level of the water suppliedinto the tub 11 through the water level sensor 34 and determines whetherthe water level is the second water level (operation 204). The controlunit 72 continues a water supply operation until the level of the watersupplied into the tub 11 reaches the second water level.

Upon completion of the water supply up to the second water level, thecontrol unit 72 detects the temperature (water temperature T) of thewater in the tub 11 through the temperature sensor 32 (operation 206).

The control unit 72 determines whether the water temperature T detectedthrough the temperature sensor 32 is greater than 0° C. (T0) and equalto or less than a first temperature T1 (about 10° C.) (operation 208).

As the determination result of operation 208, if it is determined thatthe water temperature T is greater than 0° C. (T0) and equal to or lessthan the first temperature T1 (about 10° C.), the control unit 72determines that the water temperature T is a water temperature inwinter, and performs the primary heating washing by driving the washingmotor 14 and the heater 30 (operation 210).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined firsttime period (about 25 minutes) has elapsed (operation 212).

As the determination result of operation 212, if the first time periodhas not elapsed, the control unit 72 performs the primary heatingwashing until the first time period has elapsed.

On the other hand, as the determination result of operation 212, if thefirst time period has elapsed, the control unit 72 stops the primaryheating washing by stopping the washing motor 14 and the heater 30(operation 214).

On the other hand, as the determination result of operation 208, if itis not determined that the water temperature T is greater than 0° C.(T0) and equal to or less than the first temperature T1 (about 10° C.),the control unit 72 determines whether the water temperature T detectedthrough the temperature sensor 32 is greater than the first temperatureT1 (about 10° C.) and equal to or less than a second temperature T2(about 20° C.) (operation 240).

As the determination result of operation 240, if it is determined thatthe water temperature T is greater than the first temperature T1 (about10° C.) and equal to or less than the second temperature T2 (about 20°C.), the control unit 72 determines that the water temperature T is awater temperature in spring/fall, and performs the primary heatingwashing by driving the washing motor 14 and the heater 30 (operation242).

In this case, the control unit 72 determines, as a second time period(about 20 minutes), a time period during which the water must be heatedto determine whether to drain water after the primary heating washingunder the spring/fall water temperature conditions. Then, the controlunit 72 counts the time passed since the start of the primary heatingwashing, and determines whether the predetermined second time period(about 20 minutes) has elapsed (operation 244).

As the determination result of operation 244, if the second time periodhas not elapsed, the control unit 72 performs the primary heatingwashing until the second time period has elapsed.

On the other hand, as the determination result of operation 244, if thesecond time period has elapsed, the control unit 72 proceeds tooperation 214 and stops the primary heating washing by stopping thewashing motor 14 and the heater 30.

On the other hand, as the determination result of operation 240, if itis not determined that the water temperature T is greater than the firsttemperature T1 (about 10° C.) and equal to or less than the secondtemperature T2 (about 20° C.), the control unit 72 determines whetherthe water temperature T detected through the temperature sensor 32 isgreater than the second temperature T2 (about 20° C.) (operation 250).

As the determination result of operation 250, if it is determined thatthe water temperature T is greater than the second temperature T2 (about20° C.), the control unit 72 determines that the water temperature T isa water temperature in summer, and performs the primary heating washingby driving the washing motor 14 and the heater 30 (operation 252).

In this case, the control unit 72 determines, as a third time period(about 15 minutes), a time period during which the water must be heatedto determine whether to drain water after the primary heating washingunder the summer water temperature conditions. Then, the control unit 72counts the time passed since the start of the primary heating washing,and determines whether the predetermined third time period (about 15minutes) has elapsed (operation 254).

As the determination result of operation 254, if the third time periodhas not elapsed, the control unit 72 returns to operation 152, andperforms the primary heating washing until the third time period haselapsed.

On the other hand, as the determination result of operation 254, if thethird time period has elapsed, the control unit 72 proceeds to operation214 and stops the primary heating washing by stopping the washing motor14 and the heater 30.

Thus, the primary heating washing is performed to heat the water for thefirst time period, the second time period, or the third time periodaccording to the temperature of the primarily heated water. Then, afterthe primary heating washing, whether to drain water is determinedaccording to the water temperature.

Accordingly, the control unit 72 detects the water temperature T of theprimarily heated water through the temperature sensor 32 in order todetermine whether to drain water according to the temperature of theprimarily heated water, and determines whether the detected watertemperature T is equal to or less than a predetermined third temperatureT3 (about 45° C.) (operation 216).

As the determination result of operation 216, if the water temperature Tis equal to or less than the third temperature T3 (about 45° C.), thecontrol unit 72 determines that the temperature of the primarily heatedwater is not a water temperature which may reach the target temperatureTs within the second heating time (about 35 minutes), and operates thedrain motor 22 to drain the primarily heated water (washing water)(operation 218).

Accordingly, the control unit 72 detects the level of the waterremaining in the tub 11 according to the drain operation through thewater level sensor 34, determines whether the water level is the firstwater level (operation 220), and continues the drain operation until thewater level reaches the first water level.

When the level of the water remaining in the tub 11 through the drainoperation reaches the first water level, the control unit 72 drives thewashing motor 14 and the heater 30 again and performs secondary heatingwashing to heat the water up to the target temperature Ts (about 90° C.)(operation 222).

On the other hand, as the determination result of operation 216, if thewater temperature T is greater than the third temperature T3 (about 45°C.), the control unit 72 determines that the temperature of theprimarily heated water is a water temperature which may reach the targettemperature Ts within the second heating time (about 35 minutes), anddoes not drain the primarily heated water.

Accordingly, the control unit 72 proceeds to operation 222 whilemaintaining the second water level of the primarily heated water, andperforms the secondary heating washing to heat the water up to thetarget temperature Ts by driving the washing motor 14 and the heater 30again.

Thus, if the water temperature increases according to the secondaryheating washing, the control unit 72 detects the water temperature T ofthe secondarily heated water using the temperature sensor 32, anddetermines whether the detected water temperature T is equal to orgreater than the predetermined target temperature Ts (operation 224).

As the determination result of operation 224, if the water temperature Tis less than the target temperature Ts, the control unit 72 returns tooperation 222, and continues the secondary heating washing until thewater temperature T reaches the target temperature Ts.

On the other hand, as the determination result of operation 224, if thewater temperature T is equal to or greater than the target temperatureTs, the control unit 72 stops the secondary heating washing by stoppingthe washing motor 14 and the heater 30 (operation 225).

If the water temperature T reaches the target temperature Ts, thecontrol unit 72 operates the second water supply valve 54 to supply coldwater (operation 226). When high-temperature water is drained after theboiling washing is completed, there is a possibility that the user mayget burned. Taking this possibility into consideration, a coolingprocess is performed by supplying cold water in the final stage of theboiling washing

Thus, the control unit 72 detects the water level, at which cold wateris supplied into the tub 11, through the water level sensor 34, anddetermines whether the water level is the third water level (operation228). Then, the control unit 72 continues a water supply operation untilthe level of the water supplied into the tub 11 reaches the third waterlevel.

Upon completion of the supply of cold water up to the third water level,the control unit 72 performs the process to provide a washing andcooling effect by driving the washing motor 14 for the remaining time(about 10 to 15 minutes) (operation 230), and completes the washingprocess.

Next, a method of performing a separate cooling process by supplyingcold water after washing is performed for a set time after the watertemperature T reaches the target temperature Ts will be described withreference to FIGS. 6A and 6B.

FIGS. 6A and 6B illustrate an operation flowchart showing a thirdcontrol algorithm for boiling washing in the washing machine accordingto the embodiment of the present disclosure. A repeated description ofthe same configuration as that of FIGS. 4A and 4B will be omitted.

Referring to FIGS. 6A and 6B, if the user loads the laundry(specifically, baby clothes) into the washing tub 12 and selects theboiling course button 71 provided in the input unit 70 (operation 300),the operation information selected by the user is inputted to thecontrol unit 72 through the input unit 70.

Accordingly, the control unit 72 operates the first water supply valve53 or the second water supply valve 54 through the driving unit 76 inorder to supply water (washing water) required for the boiling washingprocess.

If the first water supply valve 53 or the second water supply valve 54is operated, the first water supply valve 53 or the second water supplyvalve 54 is opened, and the water (washing water) supplied through theexternal water supply pipe passes through the first water supply pipe 51or the second water supply pipe 52 and the detergent box 48 and issupplied into the tub 11 together with the detergent (operation 302).

Accordingly, the control unit 72 detects the level of the water suppliedinto the tub 11 through the water level sensor 34 and determines whetherthe water level is the second water level (operation 304). The controlunit 72 continues a water supply operation until the level of the watersupplied into the tub 11 reaches the second water level.

Upon completion of the water supply up to the second water level, thecontrol unit 72 detects the temperature (water temperature T) of thewater in the tub 11 through the temperature sensor 32 (operation 306).

The control unit 72 determines whether the water temperature T detectedthrough the temperature sensor 32 is greater than 0° C. (T0) and equalto or less than a first temperature T1 (about 10° C.) (operation 308).

As the determination result of operation 308, if it is determined thatthe water temperature T is greater than 0° C. (T0) and equal to or lessthan the first temperature T1 (about 10° C.), the control unit 72determines that the water temperature T is a water temperature inwinter, and performs the primary heating washing by driving the washingmotor 14 and the heater 30 (operation 310).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined firsttime period (about 25 minutes) has elapsed (operation 312).

As the determination result of operation 312, if the first time periodhas elapsed, the control unit 72 stops the primary heating washing bystopping the washing motor 14 and the heater 30 (operation 314).

On the other hand, as the determination result of operation 308, if itis not determined that the water temperature T is greater than 0° C.(T0) and equal to or less than the first temperature T1 (about 10° C.),the control unit 72 determines whether the water temperature T detectedthrough the temperature sensor 32 is greater than the first temperatureT1 (about 10° C.) and equal to or less than a second temperature T2(about 20° C.) (operation 340).

As the determination result of operation 340, if it is determined thatthe water temperature T is greater than the first temperature T1 (about10° C.) and equal to or less than the second temperature T2 (about 20°C.), the control unit 72 determines that the water temperature T is awater temperature in spring/fall, and performs the primary heatingwashing by driving the washing motor 14 and the heater 30 (operation342).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined secondtime period (about 20 minutes) has elapsed (operation 344).

As the determination result of operation 344, if the second time periodhas elapsed, the control unit 72 proceeds to operation 314 and stops theprimary heating washing by stopping the washing motor 14 and the heater30.

On the other hand, as the determination result of operation 340, if itis not determined that the water temperature T is greater than the firsttemperature T1 (about 10° C.) and equal to or less than the secondtemperature T2 (about 20° C.), the control unit 72 determines whetherthe water temperature T detected through the temperature sensor 32 isgreater than the second temperature T2 (about 20° C.) and equal to orless than a third temperature T3 (about 45° C.) (operation 350).

As the determination result of operation 350, if it is determined thatthe water temperature T is greater than the second temperature T2 (about20° C.) and equal to or less than the third temperature T3 (about 45°C.), the control unit 72 determines that the water temperature T is awater temperature in summer, and performs the primary heating washing bydriving the washing motor 14 and the heater 30 (operation 352).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined thirdtime period (about 15 minutes) has elapsed (operation 354).

As the determination result of operation 354, if the third time periodhas elapsed, the control unit 72 proceeds to operation 314 and stops theprimary heating washing by stopping the washing motor 14 and the heater30.

Thus, the primary heating washing is performed to heat the water for thefirst time period, the second time period, or the third time periodaccording to the temperature of the primarily heated water. The controlunit 72 determines that the temperature of the primarily heated water isnot a water temperature which may reach the target temperature Ts withinthe second heating time (about 35 minutes), and operates the drain motor22 to drain the primarily heated water (washing water) (operation 318).

Accordingly, the control unit 72 detects the level of the waterremaining in the tub 11 according to the drain operation through thewater level sensor 34, determines whether the water level is the firstwater level (operation 320), and continues the drain operation until thewater level reaches the first water level.

Subsequently, the control unit 72 drives the washing motor 14 and theheater 30 again and performs secondary heating washing to heat the waterup to the target temperature Ts (about 90° C.) (operation 322).

On the other hand, as the determination result of operation 150, if itis not determined that the water temperature T is greater than thesecond temperature T2 (about 20° C.) and equal to or less than the thirdtemperature T3 (about 45° C.), the control unit 72 determines whetherthe water temperature T detected through the temperature sensor 32 isgreater than the third temperature T3 (about 45° C.) (operation 360).

As the determination result of operation 360, if the water temperature Tis greater than the third temperature T3 (about 20° C.), the controlunit 72 determines that the water temperature T is a water temperaturewhich may reach the target temperature Ts within the second heatingtime, and performs the primary heating washing by driving the washingmotor 14 and the heater 30 (operation 362).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined fourthtime period (about 15 minutes) has elapsed (operation 364).

As the determination result of operation 364, if the fourth time periodhas elapsed, the control unit 72 proceeds to operation 366 and stops theprimary heating washing by stopping the washing motor 14 and the heater30.

Thus, the primary heating washing is performed to heat the water for thefourth time period according to the temperature of the primarily heatedwater. The control unit 72 determines that the temperature of theprimarily heated water is a water temperature which may reach the targettemperature Ts within the second heating time (about 35 minutes), anddoes not drain the primarily heated water.

Accordingly, the control unit 72 proceeds to operation 322 whilemaintaining the second water level of the primarily heated water, andperforms the secondary heating washing to heat the water up to thetarget temperature Ts by driving the washing motor 14 and the heater 30again.

Thus, if the water temperature increases according to the secondaryheating washing, the control unit 72 detects the water temperature T ofthe secondarily heated water using the temperature sensor 32, anddetermines whether the detected water temperature T is equal to orgreater than the predetermined target temperature Ts (operation 324).

As the determination result of operation 324, if the water temperature Tis less than the target temperature Ts, the control unit 72 returns tooperation 322, and continues the secondary heating washing until thewater temperature T reaches the target temperature Ts.

On the other hand, as the determination result of operation 324, if thewater temperature T is equal to or greater than the target temperatureTs, the control unit 72 stops the secondary heating washing by stoppingthe washing motor 14 and the heater 30 (operation 325).

Then, the control unit 72 performs washing by using high-temperaturewater (washing water) after the water temperature T reaches the targettemperature Ts (operation 326). In this case, washing is performed for aset time using high-temperature water without additional consumption ofelectric energy by driving only the washing motor 14 without driving theheater 30, thereby providing a boiling washing effect to some extent.

The control unit 72 counts the washing progress time in the state of thefirst water level (or second water level) in which cold water is notsupplied after the water temperature T reaches the target temperatureTs, and determines whether a fifth time period (time period during whichwashing is additionally performed after the water temperature T reachesthe target temperature Ts to increase the washing effect, about 10 to 15minutes) has elapsed (operation 328).

As the determination result of operation 328, if the fifth time periodhas not elapsed, the control unit 72 returns to operation 326, andperforms subsequent operations.

On the other hand, as the determination result of operation 328, if thefifth time period has elapsed, the control unit 72 operates the secondwater supply valve 54 to supply cold water (operation 330). Whenhigh-temperature water is drained after the boiling washing iscompleted, there is a possibility that the user may get burned. Takingthis possibility into consideration, a cooling process is performed bysupplying cold water in the final stage of the boiling washing

Thus, the control unit 72 detects the water level, at which cold wateris supplied into the tub 11, through the water level sensor 34, anddetermines whether the water level is the third water level (operation332). Then, the control unit 72 continues a water supply operation untilthe level of the water supplied into the tub 11 reaches the third waterlevel. That is, in order to reduce the temperature of the water to atemperature (about 55 to 60° C.) suitable for drainage at which there isno risk of burns when water is drained after the boiling washing, coldwater is supplied up to the third water level.

Upon completion of the supply of cold water up to the third water level,the control unit 72 performs a separate cooling process by driving thewashing motor 14 for a set time (about 2 minutes) (operation 334), andcompletes the washing process.

Next, a method of providing a cooling effect while performing thewashing for the remaining time by supplying cold water after the watertemperature T reaches the target temperature Ts will be described withreference to FIGS. 7A and 7B.

FIGS. 7A and 7B illustrate an operation flowchart showing a fourthcontrol algorithm for boiling washing in the washing machine accordingto the embodiment of the present disclosure. A repeated description ofthe same configurations as those of FIGS. 6A and 6B will be omitted.

Referring to FIGS. 7A and 7B, if the user loads the laundry(specifically, baby clothes) into the washing tub 12 and selects theboiling course button 71 provided in the input unit 70 (operation 400),the operation information selected by the user is inputted to thecontrol unit 72 through the input unit 70.

Accordingly, the control unit 72 operates the first water supply valve53 or the second water supply valve 54 through the driving unit 76 inorder to supply water (washing water) required for the boiling washingprocess.

If the first water supply valve 53 or the second water supply valve 54is operated, the first water supply valve 53 or the second water supplyvalve 54 is opened, and the water (washing water) supplied through theexternal water supply pipe passes through the first water supply pipe 51or the second water supply pipe 52 and the detergent box 48 and issupplied into the tub 11 together with the detergent (operation 402).

Accordingly, the control unit 72 detects the level of the water suppliedinto the tub 11 through the water level sensor 34 and determines whetherthe water level is the second water level (operation 404). The controlunit 72 continues a water supply operation until the level of the watersupplied into the tub 11 reaches the second water level.

Upon completion of the water supply up to the second water level, thecontrol unit 72 detects the temperature (water temperature T) of thewater in the tub 11 through the temperature sensor 32 (operation 406).

The control unit 72 determines whether the water temperature T detectedthrough the temperature sensor 32 is greater than 0° C. (T0) and equalto or less than a first temperature T1 (about 10° C.) (operation 408).

As the determination result of operation 408, if it is determined thatthe water temperature T is greater than 0° C. (T0) and equal to or lessthan the first temperature T1 (about 10° C.), the control unit 72determines that the water temperature T is a water temperature inwinter, and performs the primary heating washing by driving the washingmotor 14 and the heater 30 (operation 410).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined firsttime period (about 25 minutes) has elapsed (operation 412).

As the determination result of operation 412, if the first time periodhas elapsed, the control unit 72 stops the primary heating washing bystopping the washing motor 14 and the heater 30 (operation 414).

On the other hand, as the determination result of operation 408, if itis not determined that the water temperature T is greater than 0° C.(T0) and equal to or less than the first temperature T1 (about 10° C.),the control unit 72 determines whether the water temperature T detectedthrough the temperature sensor 32 is greater than the first temperatureT1 (about 10° C.) and equal to or less than a second temperature T2(about 20° C.) (operation 440).

As the determination result of operation 440, if it is determined thatthe water temperature T is greater than the first temperature T1 (about10° C.) and equal to or less than the second temperature T2 (about 20°C.), the control unit 72 determines that the water temperature T is awater temperature in spring/fall, and performs the primary heatingwashing by driving the washing motor 14 and the heater 30 (operation442).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined secondtime period (about 20 minutes) has elapsed (operation 444).

As the determination result of operation 444, if the second time periodhas elapsed, the control unit 72 proceeds to operation 414 and stops theprimary heating washing by stopping the washing motor 14 and the heater30.

On the other hand, as the determination result of operation 440, if itis not determined that the water temperature T is greater than the firsttemperature T1 (about 10° C.) and equal to or less than the secondtemperature T2 (about 20° C.), the control unit 72 determines whetherthe water temperature T detected through the temperature sensor 32 isgreater than the second temperature T2 (about 20° C.) and equal to orless than a third temperature T3 (about 45° C.) (operation 450).

As the determination result of operation 450, if it is determined thatthe water temperature T is greater than the second temperature T2 (about20° C.) and equal to or less than the third temperature T3 (about 45°C.), the control unit 72 determines that the water temperature T is awater temperature in summer, and performs the primary heating washing bydriving the washing motor 14 and the heater 30 (operation 452).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined thirdtime period (about 15 minutes) has elapsed (operation 454).

As the determination result of operation 454, if the third time periodhas elapsed, the control unit 72 proceeds to operation 414 and stops theprimary heating washing by stopping the washing motor 14 and the heater30.

Thus, the primary heating washing is performed to heat the water for thefirst time period, the second time period, or the third time periodaccording to the temperature of the primarily heated water. The controlunit 72 determines that the temperature of the primarily heated water isnot a water temperature which may reach the target temperature Ts withinthe second heating time (about 35 minutes), and operates the drain motor22 to drain the primarily heated water (washing water) (operation 418).

Accordingly, the control unit 72 detects the level of the waterremaining in the tub 11 according to the drain operation through thewater level sensor 34, determines whether the water level is the firstwater level (operation 420), and continues the drain operation until thewater level reaches the first water level.

Subsequently, the control unit 72 drives the washing motor 14 and theheater 30 again and performs secondary heating washing to heat the waterup to the target temperature Ts (about 90° C.) (operation 422).

On the other hand, as the determination result of operation 450, if itis not determined that the water temperature T is greater than thesecond temperature T2 (about 20° C.) and equal to or less than the thirdtemperature T3 (about 45° C.), the control unit 72 determines whetherthe water temperature T detected through the temperature sensor 32 isgreater than the third temperature T3 (about 45° C.) (operation 460).

As the determination result of operation 460, if the water temperature Tis greater than the third temperature T3 (about 20° C.), the controlunit 72 determines that the water temperature T is a water temperaturewhich may reach the target temperature Ts within the second heatingtime, and performs the primary heating washing by driving the washingmotor 14 and the heater 30 (operation 462).

Then, the control unit 72 counts the time passed since the start of theprimary heating washing, and determines whether a predetermined fourthtime period (about 15 minutes) has elapsed (operation 464).

As the determination result of operation 464, if the fourth time periodhas elapsed, the control unit 72 stops the primary heating washing bystopping the washing motor 14 and the heater 30 (operation 466).

Thus, the primary heating washing is performed to heat the water for thefourth time period according to the temperature of the primarily heatedwater. The control unit 72 determines that the temperature of theprimarily heated water is a water temperature which may reach the targettemperature Ts within the second heating time (about 35 minutes), anddoes not drain the primarily heated water.

Accordingly, the control unit 72 proceeds to operation 422 whilemaintaining the second water level of the primarily heated water, andperforms the secondary heating washing to heat the water up to thetarget temperature Ts by driving the washing motor 14 and the heater 30again.

Thus, if the water temperature increases according to the secondaryheating washing, the control unit 72 detects the water temperature T ofthe secondarily heated water through the temperature sensor 32, anddetermines whether the detected water temperature T is equal to orgreater than the predetermined target temperature Ts (operation 424).

As the determination result of operation 424, if the water temperature Tis less than the target temperature Ts, the control unit 72 returns tooperation 422, and continues the secondary heating washing until thewater temperature T reaches the target temperature Ts.

On the other hand, as the determination result of operation 424, if thewater temperature T is equal to or greater than the target temperatureTs, the control unit 72 stops the secondary heating washing by stoppingthe washing motor 14 and the heater 30 (operation 425).

If the water temperature T reaches the target temperature Ts, thecontrol unit 72 operates the second water supply valve 54 to supply coldwater (operation 426). When high-temperature water is drained after theboiling washing is completed, there is a possibility that the user mayget burned. Taking this possibility into consideration, a coolingprocess is performed by supplying cold water in the final stage of theboiling washing.

Thus, the control unit 72 detects the water level, at which cold wateris supplied into the tub 11, through the water level sensor 34, anddetermines whether the water level is the third water level (operation428). Then, the control unit 72 continues a water supply operation untilthe level of the water supplied into the tub 11 reaches the third waterlevel.

Upon completion of the supply of cold water up to the third water level,the control unit 72 performs the process to provide a washing andcooling effect by driving the washing motor 14 for the remaining time(about 10 to 15 minutes) (operation 430), and completes the washingprocess.

Although, in the embodiment of the present disclosure, a case of settingthe target temperature Ts to 90° C. has been described as an example,the present disclosure is not limited thereto. That is, even if thetarget temperature Ts is set to equal to or greater than 70° C. at whichthe sterilizing effect begins to appear, the same object and effect asthose of the present disclosure may be achieved.

Although a few embodiments of the present disclosure have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

What is claimed is:
 1. A control method of a washing machine including atub to accommodate water and a heater installed inside the tub to heatthe water, the method comprising: determining whether a currentlywashing course is a boiling washing course; supplying water into the tubif the currently washing course is the boiling washing course;performing primary heating washing to heat the supplied water for apredetermined time; detecting a temperature of the primarily heatedwater; and controlling a level of water in the tub for secondary heatingwashing according to the detected temperature of the water, wherein thecontrolling the water level comprises varying the level of water in thetub according to the temperature of the primarily heated water.
 2. Thecontrol method according to claim 1, wherein the controlling the waterlevel comprises: comparing the temperature of the primarily heated waterwith a set temperature; and maintaining a current water level withoutdraining the primarily heated water if the temperature of the primarilyheated water is greater than the set temperature.
 3. The control methodaccording to claim 2, wherein if the temperature of the primarily heatedwater is equal to or less than the set temperature, the primarily heatedwater is drained to lower the water level.
 4. The control methodaccording to claim 3, wherein the supplying the water into the tubcomprises supplying water up to a predetermined water level for theboiling washing course.
 5. The control method according to claim 4,wherein the supplied water is cold water or hot water.
 6. The controlmethod according to claim 4, wherein the performing the primary heatingwashing comprises: detecting a temperature of the water supplied intothe tub; determining a primary heating time according to the detectedtemperature of the water; and driving the heater according to thedetermined primary heating time.
 7. The control method according toclaim 4, wherein the draining the water comprises draining the waterdown to a water level lower by one level than the predetermined waterlevel.
 8. The control method according to claim 4, further comprisingperforming secondary heating washing to heat the primarily heated waterup to a target temperature after controlling the water level.
 9. Thecontrol method according to claim 8, wherein the set temperature is atemperature of the water supplied up to the predetermined water level,which may reach the target temperature within a secondary heating time.10. The control method according to claim 9, wherein the set temperatureis about 45° C.
 11. The control method according to claim 9, wherein thetarget temperature is equal to or greater than 70° C. which may providea boiling effect.
 12. The control method according to claim 8, furthercomprising performing washing for a set time after the secondary heatingwashing.
 13. The control method according to claim 12, furthercomprising performing a cooling process by supplying cold water afterperforming the washing.
 14. The control method according to claim 8,further comprising performing a washing and cooling process by supplyingcold water after performing the secondary heating washing.
 15. A controlmethod of a washing machine including a tub to accommodate water and aheater installed inside the tub to heat the water, the methodcomprising: determining whether a currently washing course is a boilingwashing course; supplying water into the tub if the currently washingcourse is the boiling washing course; detecting a temperature of thesupplied water; determining a primary heating time according to thedetected temperature of the water; performing primary heating washing bydriving the heater according to the determined primary heating time; andcontrolling a level of water in the tub for secondary heating washingaccording to the detected temperature of the water, wherein thecontrolling the water level comprises varying the level of water in thetub according to the temperature of the supplied water.
 16. The controlmethod according to claim 15, wherein the controlling the water levelcomprises: comparing the temperature of the supplied water with a settemperature; and maintaining a current water level without draining theprimarily heated water if the temperature of the supplied water isgreater than the set temperature.
 17. The control method according toclaim 15, wherein the controlling the water level comprises: comparingthe temperature of the supplied water with a set temperature; andlowering the water level by draining the primarily heated water if thetemperature of the supplied water is equal to or less than the settemperature.
 18. The control method according to claim 15, furthercomprising, after controlling the water level, performing secondaryheating washing to heat the primarily heated water up to a targettemperature.
 19. A washing machine comprising: a tub to accommodatewater; a heater installed inside the tub to heat the water; an inputunit through which a boiling washing course is selected; a control unitto, if the boiling washing course is selected, perform primary heatingwashing for a predetermined time after supplying water into the tub,detect a temperature of the primarily heated water, and control a levelof water in the tub for secondary heating washing, wherein the controlunit varies the level of water in the tub according to the temperatureof the primarily heated water.
 20. The washing machine according toclaim 19, wherein the control unit compares the temperature of thesupplied water with a set temperature, and maintains a current waterlevel without draining the primarily heated water if the temperature ofthe supplied water is greater than the set temperature.
 21. The washingmachine according to claim 19, wherein the control unit compares thetemperature of the supplied water with a set temperature, and lowers thewater level by draining the primarily heated water if the temperature ofthe supplied water is equal to or less than the set temperature.
 22. Thewashing machine according to claim 19, wherein the control unitdetermines a primary heating time by detecting a temperature of thewater supplied into the tub, and performs primary heating washing bydriving the heater according to the determined primary heating time. 23.The washing machine according to claim 19, wherein after controlling thewater level, the control unit performs secondary heating washing to heatthe primarily heated water up to a target temperature.
 24. The washingmachine according to claim 23, wherein the control unit additionallyperforms washing for a set time after the secondary heating washing. 25.The washing machine according to claim 24, wherein the control unitperforms a cooling process by supplying cold water after the washing.26. The washing machine according to claim 23, wherein the control unitperforms a washing and cooling process by supplying cold water after thesecondary heating washing.
 27. A washing machine comprising: a tub toaccommodate water; a heater installed inside the tub to heat the water;an input unit through which a boiling washing course is selected; acontrol unit to, if the boiling washing course is selected, supply waterinto the tub, detect a temperature of the supplied water, performprimary heating washing to drive the heater for a primary heating timedetermined according to the detected temperature of the water, andcontrol a level of water in the tub for secondary heating washingaccording to the detected temperature of the water, wherein the controlunit varies the level of water in the tub according to the temperatureof the supplied water.
 28. The washing machine according to claim 27,wherein the control unit compares the temperature of the supplied waterwith a set temperature, and maintains a current water level withoutdraining the primarily heated water if the temperature of the suppliedwater is greater than the set temperature.
 29. The washing machineaccording to claim 27, wherein the control unit compares the temperatureof the supplied water with a set temperature, and lowers the water levelby draining the primarily heated water if the temperature of thesupplied water is equal to or less than the set temperature.